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SH
Section: POSIX Programmer's Manual (1P) Updated: 2013 Index
Return to Main Contents
PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
sh
--- shell, the standard command language interpreter
SYNOPSIS
sh [-abCefhimnuvx] [-o option]... [+abCefhimnuvx] [+o option]...
[command_file [argument...]]
sh -c [-abCefhimnuvx] [-o option]... [+abCefhimnuvx] [+o option]...
command_string [command_name [argument...]]
sh -s [-abCefhimnuvx] [-o option]... [+abCefhimnuvx] [+o option]...
[argument...]
DESCRIPTION
The
sh
utility is a command language interpreter that shall execute commands
read from a command line string, the standard input, or a specified
file. The application shall ensure that the commands to be executed are
expressed in the language described in
Chapter 2, Shell Command Language.
Pathname expansion shall not fail due to the size of a file.
Shell input and output redirections have an implementation-defined
offset maximum that is established in the open file description.
OPTIONS
The
sh
utility shall conform to the Base Definitions volume of POSIX.1-2008,
Section 12.2, Utility Syntax Guidelines,
with an extension for support of a leading
<plus-sign>
( '+')
as noted below.
The
-a,
-b,
-C,
-e,
-f,
-m,
-n,
-o
option,
-u,
-v,
and
-x
options are described as part of the
set
utility in
Section 2.14, Special Built-In Utilities.
The option letters derived from the
set
special built-in shall also be accepted with a leading
<plus-sign>
( '+')
instead of a leading
<hyphen>
(meaning the reverse case of the option as described in this volume of POSIX.1-2008).
The following additional options shall be supported:
- -c
-
Read commands from the
command_string
operand. Set the value of special parameter 0 (see
Section 2.5.2, Special Parameters)
from the value of the
command_name
operand and the positional parameters ($1, $2, and so on) in sequence
from the remaining
argument
operands. No commands shall be read from the standard input.
- -i
-
Specify that the shell is
interactive;
see below. An implementation may treat specifying the
-i
option as an error if the real user ID of the calling process does not
equal the effective user ID or if the real group ID does not equal the
effective group ID.
- -s
-
Read commands from the standard input.
If there are no operands and the
-c
option is not specified, the
-s
option shall be assumed.
If the
-i
option is present, or if there are no operands and the shell's standard
input and standard error are attached to a terminal, the shell is
considered to be
interactive.
OPERANDS
The following operands shall be supported:
- -
-
A single
<hyphen>
shall be treated as the first operand and then ignored. If both
'-'
and
dq--dq
are given as arguments, or if other operands precede the single
<hyphen>,
the results are undefined.
- argument
-
The positional parameters ($1, $2, and so on) shall be set to
arguments,
if any.
- command_file
-
The pathname of a file containing commands. If the pathname contains
one or more
<slash>
characters, the implementation attempts to read that file; the file need
not be executable. If the pathname does not contain a
<slash>
character:
-
- *
-
The implementation shall attempt to read that file from the current
working directory; the file need not be executable.
- *
-
If the file is not in the current working directory, the implementation
may perform a search for an executable file using the value of
PATH,
as described in
Section 2.9.1.1, Command Search and Execution.
Special parameter 0 (see
Section 2.5.2, Special Parameters)
shall be set to the value of
command_file.
If
sh
is called using a synopsis form that omits
command_file,
special parameter 0 shall be set to the value of the first argument
passed to
sh
from its parent (for example,
argv[0]
for a C program), which is normally a pathname used to execute the
sh
utility.
- command_name
-
A string assigned to special parameter 0 when executing the commands in
command_string.
If
command_name
is not specified, special parameter 0 shall be set to the value of the
first argument passed to
sh
from its parent (for example,
argv[0]
for a C program), which is normally a pathname used to execute the
sh
utility.
- command_string
-
A string that shall be interpreted by the shell as one or more
commands, as if the string were the argument to the
system()
function defined in the System Interfaces volume of POSIX.1-2008. If the
command_string
operand is an empty string,
sh
shall exit with a zero exit status.
STDIN
The standard input shall be used only if one of the following is true:
- *
-
The
-s
option is specified.
- *
-
The
-c
option is not specified and no operands are specified.
- *
-
The script executes one or more commands that require input from
standard input (such as a
read
command that does not redirect its input).
See the INPUT FILES section.
When the shell is using standard input and it invokes a command that
also uses standard input, the shell shall ensure that the standard
input file pointer points directly after the command it has read when
the command begins execution. It shall not read ahead in such a manner
that any characters intended to be read by the invoked command are
consumed by the shell (whether interpreted by the shell or not) or that
characters that are not read by the invoked command are not seen by the
shell. When the command expecting to read standard input is started
asynchronously by an interactive shell, it is unspecified whether
characters are read by the command or interpreted by the shell.
If the standard input to
sh
is a FIFO or terminal device and is set to non-blocking reads, then
sh
shall enable blocking reads on standard input. This shall remain in
effect when the command completes.
INPUT FILES
The input file shall be a text file, except that line lengths shall be
unlimited. If the input file is empty or consists solely of blank
lines or comments, or both,
sh
shall exit with a zero exit status.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of
sh:
- ENV
-
This variable, when and only when an interactive shell is invoked,
shall be subjected to parameter expansion (see
Section 2.6.2, Parameter Expansion)
by the shell, and the resulting value shall be used as a pathname of a
file containing shell commands to execute in the current environment.
The file need not be executable. If the expanded value of
ENV
is not an absolute pathname, the results are unspecified.
ENV
shall be ignored if the real and effective user IDs or real and
effective group IDs of the process are different.
- FCEDIT
-
This variable, when expanded by the shell, shall determine the default
value for the
-e
editor
option's
editor
option-argument. If
FCEDIT
is null or unset,
ed
shall be used as the editor.
- HISTFILE
-
Determine a pathname naming a command history file. If the
HISTFILE
variable is not set, the shell may attempt to access or create a file
.sh_history
in the directory referred to by the
HOME
environment variable. If the shell cannot obtain both read and
write access to, or create, the history file, it shall use an
unspecified mechanism that allows the history to operate properly.
(References to history ``file'' in this section shall be understood to
mean this unspecified mechanism in such cases.) An implementation may
choose to access this variable only when initializing the history file;
this initialization shall occur when
fc
or
sh
first attempt to retrieve entries from, or add entries to, the file, as
the result of commands issued by the user, the file named by the
ENV
variable, or implementation-defined system start-up files.
Implementations may choose to disable the history list mechanism for
users with appropriate privileges who do not set
HISTFILE;
the specific circumstances under which this occurs are
implementation-defined. If more than one instance of the shell is
using the same history file, it is unspecified how updates to the
history file from those shells interact. As entries are deleted from
the history file, they shall be deleted oldest first. It is
unspecified when history file entries are physically removed from the
history file.
- HISTSIZE
-
Determine a decimal number representing the limit to the number of
previous commands that are accessible. If this variable is unset, an
unspecified default greater than or equal to 128 shall be used. The
maximum number of commands in the history list is unspecified, but
shall be at least 128. An implementation may choose to access this
variable only when initializing the history file, as described under
HISTFILE.
Therefore, it is unspecified whether changes made to
HISTSIZE
after the history file has been initialized are effective.
- HOME
-
Determine the pathname of the user's home directory. The contents of
HOME
are used in tilde expansion as described in
Section 2.6.1, Tilde Expansion.
- IFS
-
A string treated as a list of characters that is used for field
splitting and to split lines into fields with the
read
command.
-
If
IFS
is not set, it shall behave as normal for an unset variable, except
that field splitting by the shell and line splitting by the
read
command shall be performed as if the value of
IFS
is
<space><tab><newline>;
see
Section 2.6.5, Field Splitting.
Implementations may ignore the value of
IFS
in the environment, or the absence of
IFS
from the environment, at the time the shell is invoked, in which case
the shell shall set
IFS
to
<space><tab><newline>
when it is invoked.
- LANG
-
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1-2008,
Section 8.2, Internationalization Variables
for the precedence of internationalization variables used to determine
the values of locale categories.)
- LC_ALL
-
If set to a non-empty string value, override the values of all the
other internationalization variables.
- LC_COLLATE
-
Determine the behavior of range expressions, equivalence classes, and
multi-character collating elements within pattern matching.
- LC_CTYPE
-
Determine the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments and input files), which characters
are defined as letters (character class
alpha),
and the behavior of character classes within pattern matching.
- LC_MESSAGES
-
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error.
- MAIL
-
Determine a pathname of the user's mailbox file for purposes of
incoming mail notification. If this variable is set, the shell shall
inform the user if the file named by the variable is created or if its
modification time has changed. Informing the user shall be accomplished
by writing a string of unspecified format to standard error prior to
the writing of the next primary prompt string. Such check shall be
performed only after the completion of the interval defined by the
MAILCHECK
variable after the last such check. The user shall be informed only if
MAIL
is set and
MAILPATH
is not set.
- MAILCHECK
-
Establish a decimal integer value that specifies how often (in seconds)
the shell shall check for the arrival of mail in the files specified by
the
MAILPATH
or
MAIL
variables. The default value shall be 600 seconds. If set to zero,
the shell shall check before issuing each primary prompt.
- MAILPATH
-
Provide a list of pathnames and optional messages separated by
<colon>
characters. If this variable is set, the shell shall inform the user if
any of the files named by the variable are created or if any of their
modification times change. (See the preceding entry for
MAIL
for descriptions of mail arrival and user informing.) Each pathname can
be followed by
'%'
and a string that shall be subjected to parameter expansion and written
to standard error when the modification time changes. If a
'%'
character in the pathname is preceded by a
<backslash>,
it shall be treated as a literal
'%'
in the pathname. The default message is unspecified.
-
The
MAILPATH
environment variable takes precedence over the
MAIL
variable.
- NLSPATH
-
Determine the location of message catalogs for the processing of
LC_MESSAGES.
- PATH
-
Establish a string formatted as described in the Base Definitions volume of POSIX.1-2008,
Chapter 8, Environment Variables,
used to effect command interpretation; see
Section 2.9.1.1, Command Search and Execution.
- PWD
-
This variable shall represent an absolute pathname of the current
working directory. Assignments to this variable may be ignored.
ASYNCHRONOUS EVENTS
The
sh
utility shall take the standard action for all signals (see
Section 1.4, Utility Description Defaults)
with the following exceptions.
If the shell is interactive, SIGINT signals received during command
line editing shall be handled as described in the EXTENDED DESCRIPTION,
and SIGINT signals received at other times shall be caught but no action
performed.
If the shell is interactive:
- *
-
SIGQUIT and SIGTERM signals shall be ignored.
- *
-
If the
-m
option is in effect, SIGTTIN, SIGTTOU, and SIGTSTP signals shall be
ignored.
- *
-
If the
-m
option is not in effect, it is unspecified whether SIGTTIN, SIGTTOU,
and SIGTSTP signals are ignored, set to the default action, or caught.
If they are caught, the shell shall, in the signal-catching function,
set the signal to the default action and raise the signal (after taking
any appropriate steps, such as restoring terminal settings).
The standard actions, and the actions described above for interactive
shells, can be overridden by use of the
trap
special built-in utility (see
trap
and
Section 2.11, Signals and Error Handling).
STDOUT
See the STDERR section.
STDERR
Except as otherwise stated (by the descriptions of any invoked
utilities or in interactive mode), standard error shall be used
only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
See
Chapter 2, Shell Command Language.
The functionality described in the rest of the EXTENDED DESCRIPTION
section shall be provided on implementations that support the User
Portability Utilities option
(and the rest of this section is not further shaded for this option).
Command History List
When the
sh
utility is being used interactively, it shall maintain a list of
commands previously entered from the terminal in the file named by the
HISTFILE
environment variable. The type, size, and internal format of this file
are unspecified. Multiple
sh
processes can share access to the file for a user, if file access
permissions allow this; see the description of the
HISTFILE
environment variable.
Command Line Editing
When
sh
is being used interactively from a terminal, the current command and
the command history (see
fc)
can be edited using
vi-mode
command line editing. This mode uses commands, described below,
similar to a subset of those described in the
vi
utility. Implementations may offer other command line editing modes
corresponding to other editing utilities.
The command
set
-o
vi
shall enable
vi-mode
editing and place
sh
into
vi
insert mode (see
Command Line Editing (vi-mode)).
This command also shall disable any other editing mode that the
implementation may provide. The command
set
+o
vi
disables
vi-mode
editing.
Certain block-mode terminals may be unable to support shell command
line editing. If a terminal is unable to provide either edit mode, it
need not be possible to
set
-o
vi
when using the shell on this terminal.
In the following sections, the characters
erase,
interrupt,
kill,
and
end-of-file
are those set by the
stty
utility.
Command Line Editing (vi-mode)
In
vi
editing mode, there shall be a distinguished line, the edit line. All
the editing operations which modify a line affect the edit line. The
edit line is always the newest line in the command history buffer.
With
vi-mode
enabled,
sh
can be switched between insert mode and command mode.
When in insert mode, an entered character shall be inserted into the
command line, except as noted in
vi Line Editing Insert Mode.
Upon entering
sh
and after termination of the previous command,
sh
shall be in insert mode.
Typing an escape character shall switch
sh
into command mode (see
vi Line Editing Command Mode).
In command mode, an entered character shall either invoke a defined
operation, be used as part of a multi-character operation, or be
treated as an error. A character that is not recognized as part of an
editing command shall terminate any specific editing command and shall
alert the terminal. If
sh
receives a SIGINT signal in command mode (whether generated by typing the
interrupt
character or by other means), it shall terminate command line editing
on the current command line, reissue the prompt on the next line of the
terminal, and reset the command history (see
fc)
so that the most recently executed command is the previous command
(that is, the command that was being edited when it was interrupted is
not re-entered into the history).
In the following sections, the phrase ``move the cursor to the
beginning of the word'' shall mean ``move the cursor to the first
character of the current word'' and the phrase ``move the cursor to the
end of the word'' shall mean ``move the cursor to the last character of
the current word''. The phrase ``beginning of the command line''
indicates the point between the end of the prompt string issued by the
shell (or the beginning of the terminal line, if there is no prompt
string) and the first character of the command text.
vi Line Editing Insert Mode
While in insert mode, any character typed shall be inserted in the
current command line, unless it is from the following set.
- <newline>
-
Execute the current command line. If the current command line is not
empty, this line shall be entered into the command history (see
fc).
- erase
-
Delete the character previous to the current cursor position and move
the current cursor position back one character. In insert mode,
characters shall be erased from both the screen and the buffer when
backspacing.
- interrupt
-
If
sh
receives a SIGINT signal in insert mode (whether generated by typing
the
interrupt
character or by other means), it shall terminate command line editing
with the same effects as described for interrupting command mode; see
Command Line Editing (vi-mode).
- kill
-
Clear all the characters from the input line.
- <control>-V
-
Insert the next character input, even if the character is otherwise a
special insert mode character.
- <control>-W
-
Delete the characters from the one preceding the cursor to the
preceding word boundary. The word boundary in this case is the closer
to the cursor of either the beginning of the line or a character that
is in neither the
blank
nor
punct
character classification of the current locale.
- end-of-file
-
Interpreted as the end of input in
sh.
This interpretation shall occur only at the beginning of an input
line. If
end-of-file
is entered other than at the beginning of the line, the results are
unspecified.
- <ESC>
-
Place
sh
into command mode.
vi Line Editing Command Mode
In command mode for the command line editing feature, decimal digits
not beginning with 0 that precede a command letter shall be
remembered. Some commands use these decimal digits as a count number
that affects the operation.
The term
motion command
represents one of the commands:
-
<space> 0 b F l W ^ $ ; E f T w | , B e h t
If the current line is not the edit line, any command that modifies the
current line shall cause the content of the current line to replace the
content of the edit line, and the current line shall become the edit
line. This replacement cannot be undone (see the
u
and
U
commands below). The modification requested shall then be performed to
the edit line. When the current line is the edit line, the modification
shall be done directly to the edit line.
Any command that is preceded by
count
shall take a count (the numeric value of any preceding decimal
digits). Unless otherwise noted, this count shall cause the specified
operation to repeat by the number of times specified by the count.
Also unless otherwise noted, a
count
that is out of range is considered an error condition and shall alert
the terminal, but neither the cursor position, nor the command line,
shall change.
The terms
word
and
bigword
are used as defined in the
vi
description. The term
save buffer
corresponds to the term
unnamed buffer
in
vi.
The following commands shall be recognized in command mode:
- <newline>
-
Execute the current command line. If the current command line is not
empty, this line shall be entered into the command history (see
fc).
- <control>-L
-
Redraw the current command line. Position the cursor at the same
location on the redrawn line.
- #
-
Insert the character
'#'
at the beginning of the current command line and treat the resulting
edit line as a comment. This line shall be entered into the command
history; see
fc.
- =
-
Display the possible shell word expansions (see
Section 2.6, Word Expansions)
of the bigword at the current command line position.
-
- Note:
-
This does not modify the content of the current line, and therefore
does not cause the current line to become the edit line.
These expansions shall be displayed on subsequent terminal lines. If
the bigword contains none of the characters
'?',
'*',
or
'[',
an
<asterisk>
('*')
shall be implicitly assumed at the end. If any directories are
matched, these expansions shall have a
'/'
character appended. After the expansion, the line shall be redrawn,
the cursor repositioned at the current cursor position, and
sh
shall be placed in command mode.
- \
-
Perform pathname expansion (see
Section 2.6.6, Pathname Expansion)
on the current bigword, up to the largest set of characters that can be
matched uniquely. If the bigword contains none of the characters
'?',
'*',
or
'[',
an
<asterisk>
('*')
shall be implicitly assumed at the end. This maximal expansion then
shall replace the original bigword in the command line, and the cursor
shall be placed after this expansion. If the resulting bigword
completely and uniquely matches a directory, a
'/'
character shall be inserted directly after the bigword. If some other
file is completely matched, a single
<space>
shall be inserted after the bigword. After this operation,
sh
shall be placed in insert mode.
- *
-
Perform pathname expansion on the current bigword and insert all
expansions into the command to replace the current bigword, with each
expansion separated by a single
<space>.
If at the end of the line, the current cursor position shall be moved
to the first column position following the expansions and
sh
shall be placed in insert mode. Otherwise, the current cursor position
shall be the last column position of the first character after the
expansions and
sh
shall be placed in insert mode. If the current bigword contains none
of the characters
'?',
'*',
or
'[',
before the operation, an
<asterisk>
('*')
shall be implicitly assumed at the end.
- @letter
-
Insert the value of the alias named
_letter.
The symbol
letter
represents a single alphabetic character from the portable character
set; implementations may support additional characters as an
extension. If the alias
_letter
contains other editing commands, these commands shall be performed as
part of the insertion. If no alias
_letter
is enabled, this command shall have no effect.
- [count]~
-
Convert, if the current character is a lowercase letter, to the
equivalent uppercase letter and
vice versa,
as prescribed by the current locale. The current cursor position then
shall be advanced by one character. If the cursor was positioned on
the last character of the line, the case conversion shall occur, but
the cursor shall not advance. If the
'~'
command is preceded by a
count,
that number of characters shall be converted, and the cursor shall be
advanced to the character position after the last character converted.
If the
count
is larger than the number of characters after the cursor, this shall
not be considered an error; the cursor shall advance to the last
character on the line.
- [count].
-
Repeat the most recent non-motion command, even if it was executed on
an earlier command line. If the previous command was preceded by a
count,
and no count is given on the
'.'
command, the count from the previous command shall be included as part
of the repeated command. If the
'.'
command is preceded by a
count,
this shall override any
count
argument to the previous command. The
count
specified in the
'.'
command shall become the count for subsequent
'.'
commands issued without a count.
- [number]v
-
Invoke the
vi
editor to edit the current command line in a temporary file. When the
editor exits, the commands in the temporary file shall be executed and
placed in the command history. If a
number
is included, it specifies the command number in the command history to
be edited, rather than the current command line.
- [count]l (ell)
-
- [count]<space>
-
Move the current cursor position to the next character position. If
the cursor was positioned on the last character of the line, the
terminal shall be alerted and the cursor shall not be advanced. If the
count
is larger than the number of characters after the cursor, this shall
not be considered an error; the cursor shall advance to the last
character on the line.
- [count]h
-
Move the current cursor position to the
countth
(default 1) previous character position. If the cursor was positioned
on the first character of the line, the terminal shall be alerted and
the cursor shall not be moved. If the count is larger than the number
of characters before the cursor, this shall not be considered an error;
the cursor shall move to the first character on the line.
- [count]w
-
Move to the start of the next word. If the cursor was positioned on
the last character of the line, the terminal shall be alerted and the
cursor shall not be advanced. If the
count
is larger than the number of words after the cursor, this shall not be
considered an error; the cursor shall advance to the last character on
the line.
- [count]W
-
Move to the start of the next bigword. If the cursor was positioned on
the last character of the line, the terminal shall be alerted and the
cursor shall not be advanced. If the
count
is larger than the number of bigwords after the cursor, this shall not
be considered an error; the cursor shall advance to the last character
on the line.
- [count]e
-
Move to the end of the current word. If at the end of a word, move to
the end of the next word. If the cursor was positioned on the last
character of the line, the terminal shall be alerted and the cursor
shall not be advanced. If the
count
is larger than the number of words after the cursor, this shall not be
considered an error; the cursor shall advance to the last character on
the line.
- [count]E
-
Move to the end of the current bigword. If at the end of a bigword,
move to the end of the next bigword. If the cursor was positioned on
the last character of the line, the terminal shall be alerted and the
cursor shall not be advanced. If the
count
is larger than the number of bigwords after the cursor, this shall not
be considered an error; the cursor shall advance to the last character
on the line.
- [count]b
-
Move to the beginning of the current word. If at the beginning of a
word, move to the beginning of the previous word. If the cursor was
positioned on the first character of the line, the terminal shall be
alerted and the cursor shall not be moved. If the
count
is larger than the number of words preceding the cursor, this shall not
be considered an error; the cursor shall return to the first character
on the line.
- [count]B
-
Move to the beginning of the current bigword. If at the beginning of a
bigword, move to the beginning of the previous bigword. If the cursor
was positioned on the first character of the line, the terminal shall
be alerted and the cursor shall not be moved. If the
count
is larger than the number of bigwords preceding the cursor, this shall
not be considered an error; the cursor shall return to the first
character on the line.
- ^
-
Move the current cursor position to the first character on the input
line that is not a
<blank>.
- $
-
Move to the last character position on the current command line.
- 0
-
(Zero.) Move to the first character position on the current command
line.
- [count]|
-
Move to the
countth
character position on the current command line. If no number is
specified, move to the first position. The first character position
shall be numbered 1. If the count is larger than the number of
characters on the line, this shall not be considered an error; the
cursor shall be placed on the last character on the line.
- [count]fc
-
Move to the first occurrence of the character
'c'
that occurs after the current cursor position. If the cursor was
positioned on the last character of the line, the terminal shall be
alerted and the cursor shall not be advanced. If the character
'c'
does not occur in the line after the current cursor position, the
terminal shall be alerted and the cursor shall not be moved.
- [count]Fc
-
Move to the first occurrence of the character
'c'
that occurs before the current cursor position. If the cursor was
positioned on the first character of the line, the terminal shall be
alerted and the cursor shall not be moved. If the character
'c'
does not occur in the line before the current cursor position, the
terminal shall be alerted and the cursor shall not be moved.
- [count]tc
-
Move to the character before the first occurrence of the character
'c'
that occurs after the current cursor position. If the cursor was
positioned on the last character of the line, the terminal shall be
alerted and the cursor shall not be advanced. If the character
'c'
does not occur in the line after the current cursor position, the
terminal shall be alerted and the cursor shall not be moved.
- [count]Tc
-
Move to the character after the first occurrence of the character
'c'
that occurs before the current cursor position. If the cursor was
positioned on the first character of the line, the terminal shall be
alerted and the cursor shall not be moved. If the character
'c'
does not occur in the line before the current cursor position, the
terminal shall be alerted and the cursor shall not be moved.
- [count];
-
Repeat the most recent
f,
F,
t,
or
T
command. Any number argument on that previous command shall be
ignored. Errors are those described for the repeated command.
- [count],
-
Repeat the most recent
f,
F,
t,
or
T
command. Any number argument on that previous command shall be
ignored. However, reverse the direction of that command.
- a
-
Enter insert mode after the current cursor position. Characters that
are entered shall be inserted before the next character.
- A
-
Enter insert mode after the end of the current command line.
- i
-
Enter insert mode at the current cursor position. Characters that are
entered shall be inserted before the current character.
- I
-
Enter insert mode at the beginning of the current command line.
- R
-
Enter insert mode, replacing characters from the command line beginning
at the current cursor position.
- [count]cmotion
-
Delete the characters between the current cursor position and the
cursor position that would result from the specified motion
command. Then enter insert mode before the first character following
any deleted characters. If
count
is specified, it shall be applied to the motion command. A
count
shall be ignored for the following motion commands:
-
-
0 ^ $ c
If the motion command is the character
'c',
the current command line shall be cleared and insert mode shall be
entered. If the motion command would move the current cursor position
toward the beginning of the command line, the character under the
current cursor position shall not be deleted. If the motion command
would move the current cursor position toward the end of the command
line, the character under the current cursor position shall be deleted.
If the
count
is larger than the number of characters between the current cursor
position and the end of the command line toward which the motion
command would move the cursor, this shall not be considered an error;
all of the remaining characters in the aforementioned range shall be
deleted and insert mode shall be entered. If the motion command is
invalid, the terminal shall be alerted, the cursor shall not be moved,
and no text shall be deleted.
- C
-
Delete from the current character to the end of the line and enter
insert mode at the new end-of-line.
- S
-
Clear the entire edit line and enter insert mode.
- [count]rc
-
Replace the current character with the character
'c'.
With a number
count,
replace the current and the following
count-1
characters. After this command, the current cursor position shall be
on the last character that was changed. If the
count
is larger than the number of characters after the cursor, this shall
not be considered an error; all of the remaining characters shall be
changed.
- [count]_
-
Append a
<space>
after the current character position and then append the last bigword
in the previous input line after the
<space>.
Then enter insert mode after the last character just appended. With a
number
count,
append the
countth
bigword in the previous line.
- [count]x
-
Delete the character at the current cursor position and place the
deleted characters in the save buffer. If the cursor was positioned on
the last character of the line, the character shall be deleted and the
cursor position shall be moved to the previous character (the new last
character). If the
count
is larger than the number of characters after the cursor, this shall
not be considered an error; all the characters from the cursor to the
end of the line shall be deleted.
- [count]X
-
Delete the character before the current cursor position and place the
deleted characters in the save buffer. The character under the current
cursor position shall not change. If the cursor was positioned on the
first character of the line, the terminal shall be alerted, and the
X
command shall have no effect. If the line contained a single
character, the
X
command shall have no effect. If the line contained no characters, the
terminal shall be alerted and the cursor shall not be moved. If the
count
is larger than the number of characters before the cursor, this shall
not be considered an error; all the characters from before the cursor
to the beginning of the line shall be deleted.
- [count]dmotion
-
Delete the characters between the current cursor position and the
character position that would result from the motion command. A number
count
repeats the motion command
count
times. If the motion command would move toward the beginning of the
command line, the character under the current cursor position shall not
be deleted. If the motion command is
d,
the entire current command line shall be cleared. If the
count
is larger than the number of characters between the current cursor
position and the end of the command line toward which the motion
command would move the cursor, this shall not be considered an error;
all of the remaining characters in the aforementioned range shall be
deleted. The deleted characters shall be placed in the save buffer.
- D
-
Delete all characters from the current cursor position to the end of
the line. The deleted characters shall be placed in the save buffer.
- [count]ymotion
-
Yank (that is, copy) the characters from the current cursor position to
the position resulting from the motion command into the save buffer. A
number
count
shall be applied to the motion command. If the motion command would
move toward the beginning of the command line, the character under the
current cursor position shall not be included in the set of yanked
characters. If the motion command is
y,
the entire current command line shall be yanked into the save buffer.
The current cursor position shall be unchanged. If the
count
is larger than the number of characters between the current cursor
position and the end of the command line toward which the motion
command would move the cursor, this shall not be considered an error;
all of the remaining characters in the aforementioned range shall be
yanked.
- Y
-
Yank the characters from the current cursor position to the end of the
line into the save buffer. The current character position shall be
unchanged.
- [count]p
-
Put a copy of the current contents of the save buffer after the current
cursor position. The current cursor position shall be advanced to the
last character put from the save buffer. A
count
shall indicate how many copies of the save buffer shall be put.
- [count]P
-
Put a copy of the current contents of the save buffer before the
current cursor position. The current cursor position shall be moved to
the last character put from the save buffer. A
count
shall indicate how many copies of the save buffer shall be put.
- u
-
Undo the last command that changed the edit line. This operation shall
not undo the copy of any command line to the edit line.
- U
-
Undo all changes made to the edit line. This operation shall not undo
the copy of any command line to the edit line.
- [count]k
-
- [count]-
-
Set the current command line to be the
countth
previous command line in the shell command history. If
count
is not specified, it shall default to 1. The cursor shall be positioned
on the first character of the new command. If a
k
or
-
command would retreat past the maximum number of commands in effect for
this shell (affected by the
HISTSIZE
environment variable), the terminal shall be alerted, and the command
shall have no effect.
- [count]j
-
- [count]+
-
Set the current command line to be the
countth
next command line in the shell command history. If
count
is not specified, it shall default to 1. The cursor shall be positioned
on the first character of the new command. If a
j
or
+
command advances past the edit line, the current command line shall be
restored to the edit line and the terminal shall be alerted.
- [number]G
-
Set the current command line to be the oldest command line stored in
the shell command history. With a number
number,
set the current command line to be the command line
number
in the history. If command line
number
does not exist, the terminal shall be alerted and the command line
shall not be changed.
- /pattern<newline>
-
Move backwards through the command history, searching for the specified
pattern, beginning with the previous command line. Patterns use the
pattern matching notation described in
Section 2.13, Pattern Matching Notation,
except that the
'^'
character shall have special meaning when it appears as the first
character of
pattern.
In this case, the
'^'
is discarded and the characters after the
'^'
shall be matched only at the beginning of a line. Commands in the
command history shall be treated as strings, not as filenames. If the
pattern is not found, the current command line shall be unchanged and
the terminal is alerted. If it is found in a previous line, the current
command line shall be set to that line and the cursor shall be set to
the first character of the new command line.
-
If
pattern
is empty, the last non-empty pattern provided to
/
or
?
shall be used. If there is no previous non-empty pattern, the terminal
shall be alerted and the current command line shall remain unchanged.
- ?pattern<newline>
-
Move forwards through the command history, searching for the specified
pattern, beginning with the next command line. Patterns use the pattern
matching notation described in
Section 2.13, Pattern Matching Notation,
except that the
'^'
character shall have special meaning when it appears as the first
character of
pattern.
In this case, the
'^'
is discarded and the characters after the
'^'
shall be matched only at the beginning of a line. Commands in the
command history shall be treated as strings, not as filenames. If the
pattern is not found, the current command line shall be unchanged and
the terminal alerted. If it is found in a following line, the current
command line shall be set to that line and the cursor shall be set to
the fist character of the new command line.
-
If
pattern
is empty, the last non-empty pattern provided to
/
or
?
shall be used. If there is no previous non-empty pattern, the terminal
shall be alerted and the current command line shall remain unchanged.
- n
-
Repeat the most recent
/
or
?
command. If there is no previous
/
or
?,
the terminal shall be alerted and the current command line shall remain
unchanged.
- N
-
Repeat the most recent
/
or
?
command, reversing the direction of the search. If there is no previous
/
or
?,
the terminal shall be alerted and the current command line shall remain
unchanged.
EXIT STATUS
The following exit values shall be returned:
- 0
-
The script to be executed consisted solely of zero or more blank lines
or comments, or both.
- 1-125
-
A non-interactive shell detected an error other than
command_file
not found, including but not limited to syntax, redirection, or variable
assignment errors.
- 127
-
A specified
command_file
could not be found by a non-interactive shell.
Otherwise, the shell shall return the exit status of the last command
it invoked or attempted to invoke (see also the
exit
utility in
Section 2.14, Special Built-In Utilities).
CONSEQUENCES OF ERRORS
See
Section 2.8.1, Consequences of Shell Errors.
The following sections are informative.
APPLICATION USAGE
Standard input and standard error are the files that
determine whether a shell is interactive when
-i
is not specified. For example:
-
sh > file
and:
-
sh 2> file
create interactive and non-interactive shells, respectively. Although
both accept terminal input, the results of error conditions are
different, as described in
Section 2.8.1, Consequences of Shell Errors;
in the second example a redirection error encountered by a special
built-in utility aborts the shell.
A conforming application must protect its first operand, if it starts
with a
<plus-sign>,
by preceding it with the
dq--dq
argument that denotes the end of the options.
Applications should note that the standard
PATH
to the shell cannot be assumed to be either
/bin/sh
or
/usr/bin/sh,
and should be determined by interrogation of the
PATH
returned by
getconf
PATH,
ensuring that the returned pathname is an absolute pathname and not a
shell built-in.
For example, to determine the location of the standard
sh
utility:
-
command -v sh
On some implementations this might return:
-
/usr/xpg4/bin/sh
Furthermore, on systems that support executable scripts (the
dq#!dq
construct), it is recommended that applications using executable
scripts install them using
getconf
PATH
to determine the shell pathname and update the
dq#!dq
script appropriately as it is being installed (for example, with
sed).
For example:
-
#
# Installation time script to install correct POSIX shell pathname
#
# Get list of paths to check
#
Sifs=$IFS
Sifs_set=${IFS+y}
IFS=:
set -- $(getconf PATH)
if [ "$Sifs_set" = y ]
then
IFS=$Sifs
else
unset IFS
fi
#
# Check each path for 'sh'
#
for i
do
if [ -x "${i}"/sh ]
then
Pshell=${i}/sh
fi
done
#
# This is the list of scripts to update. They should be of the
# form '${name}.source' and will be transformed to '${name}'.
# Each script should begin:
#
# #!INSTALLSHELLPATH
#
scripts="a b c"
#
# Transform each script
#
for i in ${scripts}
do
sed -e "s|INSTALLSHELLPATH|${Pshell}|" < ${i}.source > ${i}
done
EXAMPLES
- 1.
-
Execute a shell command from a string:
-
-
sh -c "cat myfile"
- 2.
-
Execute a shell script from a file in the current directory:
-
-
sh my_shell_cmds
RATIONALE
The
sh
utility and the
set
special built-in utility share a common set of options.
The name
IFS
was originally an abbreviation of ``Input Field Separators''; however,
this name is misleading as the
IFS
characters are actually used as field terminators. The KornShell
ignores the contents of
IFS
upon entry to the script. A conforming application cannot rely on
importing
IFS.
One justification for this, beyond security considerations, is to
assist possible future shell compilers. Allowing
IFS
to be imported from the environment prevents many optimizations that
might otherwise be performed via dataflow analysis of the script
itself.
The text in the STDIN section about non-blocking reads concerns an
instance of
sh
that has been invoked, probably by a C-language program, with standard
input that has been opened using the O_NONBLOCK flag; see
open()
in the System Interfaces volume of POSIX.1-2008. If the shell did not reset this flag, it would
immediately terminate because no input data would be available yet and
that would be considered the same as end-of-file.
The options associated with a
restricted shell
(command name
rsh
and the
-r
option) were excluded because the standard developers considered that
the implied level of security could not be achieved and they did not
want to raise false expectations.
On systems that support set-user-ID scripts,
a historical trapdoor has been to link a script to the name
-i.
When it is called by a sequence such as:
-
sh -
or by:
-
#! usr/bin/sh -
the historical systems have assumed that no option letters follow.
Thus, this volume of POSIX.1-2008 allows the single
<hyphen>
to mark the end of the options, in addition to the use of the regular
dq--dq
argument, because it was considered that the older practice was so
pervasive. An alternative approach is taken by the KornShell, where
real and effective user/group IDs must match for an interactive shell;
this behavior is specifically allowed by this volume of POSIX.1-2008.
- Note:
-
There are other problems with set-user-ID scripts that the two
approaches described here do not resolve.
The initialization process for the history file can be dependent on the
system start-up files, in that they may contain commands that
effectively preempt the user's settings of
HISTFILE
and
HISTSIZE.
For example, function definition commands are recorded in the history
file, unless the
set
-o
nolog
option is set. If the system administrator includes function
definitions in some system start-up file called before the
ENV
file, the history file is initialized before the user gets a chance to
influence its characteristics. In some historical shells, the history
file is initialized just after the
ENV
file has been processed. Therefore, it is implementation-defined
whether changes made to
HISTFILE
after the history file has been initialized are effective.
The default messages for the various
MAIL-related
messages are unspecified because they vary across implementations.
Typical messages are:
-
"you have mail\n"
or:
-
"you have new mail\n"
It is important that the descriptions of command line editing refer to
the same shell as that in POSIX.1-2008 so that interactive users can also be
application programmers without having to deal with programmatic
differences in their two environments. It is also essential that the
utility name
sh
be specified because this explicit utility name is too firmly rooted in
historical practice of application programs for it to change.
Consideration was given to mandating a diagnostic message when
attempting to set
vi-mode
on terminals that do not support command line editing. However, it is
not historical practice for the shell to be cognizant of all terminal
types and thus be able to detect inappropriate terminals in all cases.
Implementations are encouraged to supply diagnostics in this case
whenever possible, rather than leaving the user in a state where
editing commands work incorrectly.
In early proposals, the KornShell-derived
emacs
mode of command line editing was included, even though the
emacs
editor itself was not. The community of
emacs
proponents was adamant that the full
emacs
editor not be standardized because they were concerned that an attempt
to standardize this very powerful environment would encourage vendors
to ship strictly conforming versions lacking the extensibility required
by the community. The author of the original
emacs
program also expressed his desire to omit the program. Furthermore,
there were a number of historical systems that did not include
emacs,
or included it without supporting it, but there were very few that did
not include and support
vi.
The shell
emacs
command line editing mode was finally omitted because it became
apparent that the KornShell version and the editor being distributed
with the GNU system had diverged in some respects. The author of
emacs
requested that the POSIX
emacs
mode either be deleted or have a significant number of unspecified
conditions. Although the KornShell author agreed to consider changes to
bring the shell into alignment, the standard developers decided to
defer specification at that time. At the time, it was assumed that
convergence on an acceptable definition would occur for a subsequent
draft, but that has not happened, and there appears to be no impetus to
do so. In any case, implementations are free to offer additional
command line editing modes based on the exact models of editors their
users are most comfortable with.
Early proposals had the following list entry in
vi Line Editing Insert Mode:
- \
-
If followed by the
erase
or
kill
character, that character shall be inserted into the input line.
Otherwise, the
<backslash>
itself shall be inserted into the input line.
However, this is not actually a feature of
sh
command line editing insert mode, but one of some historical terminal
line drivers. Some conforming implementations continue to do this when
the
stty
iexten
flag is set.
In interactive shells, SIGTERM is ignored so that
kill 0
does not kill the shell, and SIGINT is caught so that
wait
is interruptible. If the shell does not ignore SIGTTIN, SIGTTOU, and
SIGTSTP signals when it is interactive and the
-m
option is not in effect, these signals suspend the shell if it is not
a session leader. If it is a session leader, the signals are discarded
if they would stop the process, as required by the System Interfaces volume of POSIX.1-2008,
Section 2.4.3, Signal Actions
for orphaned process groups.
FUTURE DIRECTIONS
None.
SEE ALSO
Chapter 2, Shell Command Language,
cd,
echo,
exit,
fc,
pwd,
invalid,
set,
stty,
test,
trap,
umask,
vi
The Base Definitions volume of POSIX.1-2008,
Chapter 8, Environment Variables,
Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1-2008,
dup(),
exec,
exit(),
fork(),
open(),
pipe(),
signal(),
system(),
ulimit(),
umask(),
wait()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- OPERANDS
-
- STDIN
-
- INPUT FILES
-
- ENVIRONMENT VARIABLES
-
- ASYNCHRONOUS EVENTS
-
- STDOUT
-
- STDERR
-
- OUTPUT FILES
-
- EXTENDED DESCRIPTION
-
- Command History List
-
- Command Line Editing
-
- Command Line Editing (vi-mode)
-
- vi Line Editing Insert Mode
-
- vi Line Editing Command Mode
-
- EXIT STATUS
-
- CONSEQUENCES OF ERRORS
-
- APPLICATION USAGE
-
- EXAMPLES
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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